The first half of the 20th century saw a dramatic shift in naval warfare and the types of ships that were used in conflict at sea. Changing nature of naval warfare In 1906, the HMS Dreadnought battleship revolutionized naval warfare, as it was steam powered, incredibly fast for its size, quickly built, and its primary battery of guns was mounted on the main deck. The HMS Dreadnought then inspired virtually all battleships that came after it, in what would become a naval arms race, but as technology advanced in the interwar period, some proposed that aircraft carriers should become the most important ships in the navy. While the attack on Pearl Harbor would highlight the effectiveness of naval air power, and battleships themselves were among the primary targets in the attack, it was not until 1942 at battles such as Midway or the Battle of the Coral Sea where the aircraft carrier established itself as the heart of the navy. Battleships, as well as cruisers or destroyers, largely played a supporting role for the remainder of the war, and (apart from two events) major naval battles became a thing of the past after WWII. Ascendancy of the U.S. Navy Another significant development of WWII was the emergence of the United States as the world's foremost naval power. During the war, the U.S. built almost 9,000 war vessels (not including landing vessels), which was more than three times the amount of all other powers combined. U.S. production capacity meant that it was able to continually produce and replace major vessels as the war waged on. In contrast, the Japanese did not have the ability to replace lost or damaged ships, which contributed to their eventual defeat in the Pacific. In Europe, the conflict was much more concentrated on land; however, the German Navy prioritized the production of submarines, which it used to great effect when attacking transatlantic shipping that supplied the UK - the Battle of the Atlantic would largely be settled by the end of 1943, with the Royal Navy and Commonwealth forces sinking over half of all German U-boats.

This volume contains enlargements of warship diagrams taken from the journal Engineering and the 1941 edition of the arms catalogue Jane's Fighting Ships. The source of each photograph is cited (usually on the back of the photograph). There are further notes either on the face of the photograph or on the back. These give further details about the size of the ship and its displacement. There are a small number of clippings from periodicals attached to the photographs which give further information about the ship or photographs of it. The diagrams usually show the elevations of the ship indicating its length, and a diagram of the lay-out below the deck. Below the diagram there is a heading 'machinery' which indicates the type of engines, boilers and other equipment held on the ship.

The Royal Navy ships detailed include the battleships of the -

* King George V Class (representing HMS King George V, HMS Duke of York, HMS Anson and HMS Howe)
* Nelson Class (representing HMS Nelson and HMS Rodney)
* Royal Sovereign Class (representing HMS Royal Sovereign, HMS Resolution, HMS Ramillies, and HMS Revenge)
* Queen Elizabeth Class (representing HMS Queen Elizabeth and HMS Warspite)

along with the battlecruisers HMS Renown, HMS Repulse, and HMS Hood plus the Aircraft Carriers of the -

* Illustrious Class (representing HMS Illustrious, HMS Victorious, HMS Formidable, and HMS Indomitable)
* HMS Courageous and HMS Glorious (battleships later converted into Aircraft Carriers)
* HMS Furious (initially a cruiser and then as an Aircraft Carrier) plus light cruisers of the -

* Leander Class (representing HMS Leander, HMS Orion, HMS Achilles, and HMS Ajax).

United States Navy battleships detailed include the battleships of the -

* Washington Class (representing the USS North Carolina, USS Washington, USS Indiana, USS Massachusetts, USS Alabama, and USS South Dakota)
* New Mexico Class (representing the USS Idaho, Mississippi, and USS New Mexico)
* California Class (representing the USS California and USS Tennessee)

along with the Aircraft Carriers - USS Lexington, USS Saratoga, USS Wasp, USS Enterprise, USS Hornet, and USS Yorktown and the Cruisers of the -

* Northampton Class (representing the USS Augusta, USS Chester, USS Chicago, USS Houston, USS Louisville, and USS Northampton)
* Brooklyn Class (representing the USS Brooklyn, USS Philadelphia, USS Savannah, USS Nashville, USS Phoenix, USS Boise, USS Honolulu, USS Helena, and USS St Louis.
* Portland Class (representing the USS Portland and USS Indianapolis)

The Royal Australian Navy Ships include the heavy cruisers HMAS Australia, HMAS Canberra, plus the light cruisers HMAS Perth (formerly HMS Amphion) and the HMAS Hobart (formerly the HMS Apollo).

In 2022, there were 327,934 active duty Navy members in the United States Department of Defense. This represents a slight decrease in comparison to the amount recorded in the previous year. In comparison, there were 449,344 active duty U.S. Army members that same year.

For the fiscal year of 2025, the U.S. Navy had a proposed budget of about ****** billion U.S. dollars, an increase from the previous year. This is compared to the U.S. Marine Corps, which had about ***** billion U.S. dollars at their disposal.